There is a contents distributing system for distributing contents data, such as music, over the network, such as EMD (electronic music distribution). With this system, a user terminal device, for example, may access a server device, where the contents data are stored, to download desired contents data. For payment, the private information, such as a credit card number, a secret number or the Web money, is sent from the user terminal device to the server device.
In such system, payment is by transmitting the private information, such as credit card number, secret number or the Web money from the terminal device to the server device, over the network, so that a cumbersome operation is needed in inputting the private information. Moreover, there is a risk that the private information may be illicitly acquired by a third party for unauthorized use.
As a means for combating this problem, there is a payment system employing a pre-paid recording medium. In this system, the remaining recordable volume of the contents data is recorded on the recording medium purchased by the user. When the terminal device accesses a server device to download the contents data desired by the user, data indicating the recordable volume is transmitted from the terminal device to the server device. The terminal device receives the downloaded contents data and the updated data indicating the recordable data volume to record these data on the recording medium.
With the recording medium used in this system, the contents data and the data indicating the recordable data volume need to be updated from time to time, and hence the write-once or rewritable recording medium is used. Consequently, the recordable data volume, recorded on the recording medium, may be manipulated by a user with a malignant intention, as a result of which the contents data may be repeatedly downloaded by the user with a malignant intention, thus detracting from the benefit of the system supervisor or the copyright owner.